Citation: Sphenolithaceae Deflandre 1952Taxonomic rank: familyTaxonomic discussion: We follow Howe (2021) in subdividing the family into two genera - Sphenolithus and Furcatolithus. The genus Furcatolithus comprises the predistentus-distentus-ciperoensis lineage, which is clearly separated from the other sphenoliths.
Distinguishing features: Parent taxon (Discoasterales): Radially symmetrical nannoliths formed from one to several separate cycles of elements that radiate from a common centre or axis. This taxon: Conical discoasteralids with a concave base, consisting of a mass of elements radiating from a common origin.
Original description: Sphénolithes, ou corpuscules en coin, à structure sphérolithique parliculière, donnant en lumière polarisée une croix noire en position longitudinale
Sphenolith structure: The individual elements of sphenoliths are elongated parallel to their c-axis (this is clear from light microscopy), and consist of three lath-like blades arranged in a Y-shaped form. This morphology is visible in SEMs of specimens from samples with very good preservation, or slight etching. With overgrowth the spaces between the segments become infilled and the elements develop a spinose form. The triple lath form is probably related to the trigonal symmetry of calcite, with laths developing parallel to the x-axes. The elements radiate from a single origin, which gives the sphenoliths a compact form, and a clear extinction-cross, in polarized light. The proximal part of all sphenolith species is composed of a single cycle of 8 to 16 of these elements. The axes of the proximal elements slope down from the median plane. A concave base is formed by laths from adjacent elements meeting. The upper half of sphenoliths is normally formed of two or three cycles of elements, radiating from the centre, at decreasing angles to the vertical. The details of the structure are, however, variable; particularly toward the apex, which gives rise to a large amount of species level variation. See Howe 2021 for updated discussion.
Phylogenetic relationsSphenoliths first appear in the Palaeocene and go extinct in the mid Pliocene. They show some similarities to Fasciculithaceae and are thought to have similar origins.
Howe 2021 f07.JPG
Howe 2021 f08.JPG
Howe 2021 f09.JPG
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Howe 2021 fig11.JPG
Search data:
Lith size: 2->20µm;
The morphological data given here can be used on the advanced search page. See also these notes
Geological Range: Last occurrence (top): at top of NN16 zone (100% up, 2.5Ma, in Gelasian stage). Data source: Total of ranges of the species in this database First occurrence (base): within NP4 zone (61.51-63.25Ma, base in Danian stage). Data source: Total of ranges of species in this database
Plot of occurrence data:
Range-bar - range as quoted above, pink interval top occurs in, green interval base occurs in.
Triangles indicate an event for which a precise placement has been suggested
Neptune data: this is a higher taxon page so Neptune data is not plotted. For the customisable plot option go to a genus page Parent: Discoasterales
References:
Deflandre, G. (1952). Classe des Coccolithophoridés. (Coccolithophoridae. Lohmann, 1902). In, Grassé, P. P. (ed.) Traité de Zoologie. Masson, Paris 439-470. gs
Howe, R. (2021). Ultrastructure and taxonomy of the family Sphenolithaceae. Journal of Nannoplankton Research. 39(1): 29-75. gsO
Perch-Nielsen, K. (1985). Cenozoic calcareous nannofossils. In, Bolli, H. M., Saunders, J. B. & Perch-Nielsen, K. (eds) Plankton Stratigraphy. Cambridge University Press, Cambridge (1): 427-555. gs
Sphenolithaceae compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 11-7-2025
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